diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 42dedfcee526a1b1c8f69d55317e0df717f744d1..ce4a9575a514ed7ffe1f862c3a56b01cd0b782f7 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,5 +1,14 @@
2016-11-15 Jonathan Wakely <jwakely@redhat.com>
+ * doc/xml/manual/intro.xml: Document LWG 2742 status.
+ * doc/html/*: Regenerate.
+ * include/bits/basic_string.h
+ (basic_string(const T&, size_type, size_type, const Allocator&)): Add
+ constructor for substring of basic_string_view, as per LWG 2742 but
+ with additional constraint to fix ambiguity.
+ * testsuite/21_strings/basic_string/cons/char/9.cc: New test.
+ * testsuite/21_strings/basic_string/cons/wchar_t/9.cc: New test.
+
* doc/xml/manual/intro.xml: Document LWG 2748 status.
* include/std/optional (optional<T>::swap): Use is_nothrow_swappable_v
for exception specification.
diff --git a/libstdc++-v3/doc/html/manual/bugs.html b/libstdc++-v3/doc/html/manual/bugs.html
index 122bf8f7b9fe0f25006b64801a2606c19068240a..d4a39d82e896196a770349a120e6c161e99ddac2 100644
--- a/libstdc++-v3/doc/html/manual/bugs.html
+++ b/libstdc++-v3/doc/html/manual/bugs.html
@@ -496,11 +496,21 @@
</span></dt><dd><p>Avoid using <code class="code">dynamic_cast</code> when it would be
ill-formed.
</p></dd><dt><span class="term"><a class="link" href="../ext/lwg-defects.html#2583" target="_top">2583</a>:
- <span class="emphasis"><em>There is no way to supply an allocator for <code class="code"> basic_string(str, pos)</code>
+ <span class="emphasis"><em>There is no way to supply an allocator for <code class="code">basic_string(str, pos)</code>
</em></span>
</span></dt><dd><p>Add new constructor
</p></dd><dt><span class="term"><a class="link" href="../ext/lwg-defects.html#2684" target="_top">2684</a>:
<span class="emphasis"><em><code class="code">priority_queue</code> lacking comparator typedef
</em></span>
</span></dt><dd><p>Define the <code class="code">value_compare</code> typedef.
+ </p></dd><dt><span class="term"><a class="link" href="../ext/lwg-defects.html#2742" target="_top">2742</a>:
+ <span class="emphasis"><em>Inconsistent <code class="code">string</code> interface taking <code class="code">string_view</code>
+ </em></span>
+ </span></dt><dd><p>Add the new constructor and additionally constrain it
+ to avoid ambiguities with non-const <code class="code">charT*</code>.
+ </p></dd><dt><span class="term"><a class="link" href="../ext/lwg-defects.html#2748" target="_top">2748</a>:
+ <span class="emphasis"><em>swappable traits for optionals
+ </em></span>
+ </span></dt><dd><p>Disable the non-member <code class="code">swap</code> overload when
+ the contained object is not swappable.
</p></dd></dl></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="license.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="status.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="setup.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">License </td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 2. Setup</td></tr></table></div></body></html>
\ No newline at end of file
diff --git a/libstdc++-v3/doc/xml/manual/intro.xml b/libstdc++-v3/doc/xml/manual/intro.xml
index 0df24bb5f2f93809f7864c17935363c4e01eda76..7f2586d816045881ca99cdba0a2c9823f36950eb 100644
--- a/libstdc++-v3/doc/xml/manual/intro.xml
+++ b/libstdc++-v3/doc/xml/manual/intro.xml
@@ -1107,6 +1107,14 @@ requirements of the license of GCC.
<listitem><para>Define the <code>value_compare</code> typedef.
</para></listitem></varlistentry>
+ <varlistentry><term><link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="../ext/lwg-defects.html#2742">2742</link>:
+ <emphasis>Inconsistent <code>string</code> interface taking <code>string_view</code>
+ </emphasis>
+ </term>
+ <listitem><para>Add the new constructor and additionally constrain it
+ to avoid ambiguities with non-const <code>charT*</code>.
+ </para></listitem></varlistentry>
+
<varlistentry><term><link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="../ext/lwg-defects.html#2748">2748</link>:
<emphasis>swappable traits for optionals
</emphasis>
diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h
index b80e2705c29aa9d1066f27c80f6bfd37fc1f0f26..943e88d87228a699c4e4798e3817763790e5c1af 100644
--- a/libstdc++-v3/include/bits/basic_string.h
+++ b/libstdc++-v3/include/bits/basic_string.h
@@ -585,13 +585,28 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
{ _M_construct(__beg, __end); }
#if __cplusplus > 201402L
+ /**
+ * @brief Construct string from a substring of a string_view.
+ * @param __t Source string view.
+ * @param __pos The index of the first character to copy from __t.
+ * @param __n The number of characters to copy from __t.
+ * @param __a Allocator to use.
+ */
+ template<typename _Tp, typename =
+ _Require<is_convertible<_Tp, __sv_type>,
+ __not_<is_convertible<const _Tp&, const _CharT*>>>>
+ basic_string(const _Tp& __t, size_type __pos, size_type __n,
+ const _Alloc& __a = _Alloc())
+ : basic_string(__sv_type(__t).substr(__pos, __n), __a) { }
+
/**
* @brief Construct string from a string_view.
* @param __sv Source string view.
* @param __a Allocator to use (default is default allocator).
*/
- explicit basic_string(__sv_type __sv, const _Alloc& __a = _Alloc())
- : basic_string(__sv.data(), __sv.size(), __a) {}
+ explicit
+ basic_string(__sv_type __sv, const _Alloc& __a = _Alloc())
+ : basic_string(__sv.data(), __sv.size(), __a) { }
#endif // C++17
/**
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/9.cc b/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/9.cc
new file mode 100644
index 0000000000000000000000000000000000000000..0024ffc889441482741fc3979d067217f2b1c4b1
--- /dev/null
+++ b/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/9.cc
@@ -0,0 +1,46 @@
+// Copyright (C) 2016 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library. This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3. If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++17" }
+// { dg-do run { target c++1z } }
+
+#include <string>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+ using C = char;
+ using string_type = std::basic_string<C>;
+ using view_type = std::basic_string_view<C>;
+
+ std::allocator<C> alloc;
+ VERIFY( string_type(view_type("string")) == "string" );
+ VERIFY( string_type(view_type("string"), alloc) == "string" );
+
+ // LWG 2742
+ VERIFY( string_type("substring", 3, 6) == "string" );
+ VERIFY( string_type("substring", 3, 6, alloc) == "string" );
+ VERIFY( string_type(view_type("substring"), 3, 6) == "string" );
+ VERIFY( string_type(view_type("substring"), 3, 6, alloc) == "string" );
+}
+
+int
+main()
+{
+ test01();
+}
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/cons/wchar_t/9.cc b/libstdc++-v3/testsuite/21_strings/basic_string/cons/wchar_t/9.cc
new file mode 100644
index 0000000000000000000000000000000000000000..bf4b4403ad15f7bb77e3a7a1e7b93594b46605e9
--- /dev/null
+++ b/libstdc++-v3/testsuite/21_strings/basic_string/cons/wchar_t/9.cc
@@ -0,0 +1,46 @@
+// Copyright (C) 2016 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library. This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3. If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++17" }
+// { dg-do run { target c++1z } }
+
+#include <string>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+ using C = wchar_t;
+ using string_type = std::basic_string<C>;
+ using view_type = std::basic_string_view<C>;
+
+ std::allocator<C> alloc;
+ VERIFY( string_type(view_type(L"string")) == L"string" );
+ VERIFY( string_type(view_type(L"string"), alloc) == L"string" );
+
+ // LWG 2742
+ VERIFY( string_type(L"substring", 3, 6) == L"string" );
+ VERIFY( string_type(L"substring", 3, 6, alloc) == L"string" );
+ VERIFY( string_type(view_type(L"substring"), 3, 6) == L"string" );
+ VERIFY( string_type(view_type(L"substring"), 3, 6, alloc) == L"string" );
+}
+
+int
+main()
+{
+ test01();
+}